1. Field of the Invention
This invention relates to dynamoelectric machines, and more particularly, to means for liquidly cooling the field winding thereof.
2. Description of the Prior Art
Dynamoelectric machines, such as turbine generators, are often designed such that the steel in their rotors is operated near magnetic saturation. Rating increases for dynamoelectric machines of given size operated near such limit are made possible only by raising the magnetic saturation limit of the rotor. The magnetic saturation limit of a dynamoelectric machine's rotor can be increased by reducing the depth of coil slots formed in the rotor. Liquidly cooled coils can be operated at higher excitation current levels than those which are gas cooled and, thus, liquid coolant permits the use of shallower coil slots than are required by gas coolant. In general, the superior cooling properties of liquid coolant over those of gaseous coolant permit the higher I.sup.2 R losses in liquidly cooled coils to be carried away so as to maintain the temperature in the rotor below the critical temperature at which the coil's insulation loses adequate strength and the electrical conductors lose adequate fatigue resistance properties. It can be shown that liquidly cooled rotors can increase generator efficiency substantially over equivalently sized gaseous cooled rotors.
Transmitting liquid coolant to, through, and from rotor coils requires the use of conduits. Conventional manifolding techniques for distribution and collection of the liquid coolant would involve disposing distribution and discharge chambers at axially opposite ends of the rotor. The previously mentioned conduits connect the respective chambers to the heat generating rotor coils. Conventional generator rotor construction utilizes retaining ring structures at both axial ends of a rotor to restrain radial movement of coil end turns in making their turnaround between longitudinal slots situated on opposite circumferential sides of the particular rotor pole. Use of such conduits between the chambers and rotor coils requires securing those conduits along with the insulation which isolates the coils from the chambers, radially beneath the retaining rings. As such, liquid coolant leaks or electrical grounds are difficult to locate and very expensive to correct. Other inconveniences and disadvantages of the end turn retaining rings which are customarily shrunk-fit onto the ends of generator rotors include undesirable bending stresses in the copper rotor coils resulting from cycling deflection of the retaining rings, increased difficulty in bracing the liquid coolant conduits, and increased complexity in assembling and disassembling the end plates which help maintain the retaining ring's round configuration. Such greater complexity results from the requirement that the plates clear the rotor shaft during assembly and disassembly so as to avoid interfering with the conduits and their insulators.
Elimination of generator retaining rings is therefore believed desirable, and is, in fact, disclosed in copending Westinghouse Electric Case No. 44,973, whose Ser. No. is 877,778, and filing date is Feb. 14, 1978. Elimination of such retaining rings and introduction of embedded field winding end turns necessitates development of a cooling scheme which is compatible therewith.